In the aftermath of the Southern hemisphere harvest, some poor unfortunates are still struggling with stuck fermentations. In most cases when looking at the facts one can pinpoint why the stuck occurred, but on the odd occasion the reason is not very clear. I had a situation last week where the winemaker, who also happens to be a consultant to other winemakers, had one of these un-explainable stucks. (I think I’ve just created a new word.) He did everything by the book, made all the right choices, grapes were of good quality, etc. Naturally, the first instinct of winemakers when they see the RS remaining the same for more than a week is to consider re-inoculation. Now, this is where the good news comes in. It seems that there is a miracle product, called yeast hulls, which can potentially save you this costly, time consuming, hair pulling, teeth gnashing, and no guarantee that it will work experience.
Yeast companies recommend the use of pure yeast hulls as part of a re-inoculation protocol. The science behind it is that the yeast that got stuck was under stress to survive and as a result produced medium chain fatty acids. These medium chain fatty acids are toxic to the fermenting yeast as well as to the new yeast used for re-inoculation, as well as to MLF bacteria. So one has to “detoxify” the must first before inoculating with new yeast. The recommended contact time with yeast hulls before starting the re-inoculation process is 48 hours.
However, I have seen on more than one occasion that the addition of yeast hulls can lift the inhibition on the stuck yeast, with fermentation starting again and completing without the need to re-inoculate. Over time I have come to identify a possible scenario where such a phenomenon is possible. It seems that if the total yeast count is more than one million cells per ml and the yeast viability is 30% or more, then there is a chance that the fermentation might pull through. Depending on the other existing must conditions it might not be possible for the fermentation to go bone dry, but it might get the wine into a “blendable” (another new word? poor English?) condition.
In the particular case I dealt with last week the wine had an RS of 12 g/l. The wine was stuck at that sugar for over a week. The winemaker added Bio-Springer yeast hulls at 40 g/hl and the residual sugar went down to 3 g/l in less than a week. His yeast cell count and viability were over one million cells per ml and 30% respectively. In other cases that I am aware off where yeast hulls allowed fermentation to complete, the product Extraferm from Oenobrands was used at a dosage of 50 g/hl.